Hard asphalt fluxes are available in relatively large quantities and could provide a useful and inexpensive source of asphalt for use in making coating grade asphalt if means could be found for modifying the flux properties so that, after airblowing, the essential combination of softening point and penetration value is obtained without loss of other important properties.
In conventional practice, asphalt flux is air blown, in the presence or absence of a catalyst, in order to modify the properties of the flux as needed for a desired use. Certain types of asphalt flux can be air-blown in this fashion to give the right combination of softening point and penetration required for coating grade asphalt (also called "roofing grade asphalt" or just "roofing asphalt"). Desirably, for example, coating grade asphalt has a softening point of about 200-225.degree. F. and a penetration value of 16-22 although the penetration can be a point or two lower where the softening point is on the high side of the indicated range or even higher, e.g. 230-235.degree. F.
Some asphalt fluxes, however, cannot be airblown, with or without a catalyst, to give the softening point and penetration properties essential for use as coating grade or roofing asphalt. Typical of these fluxes are paving grade asphalt, California hard flux and the like. For example, paving grade asphalt flux known as AC-20, when air blown without a catalyst, gives a softening point of about 214.degree. F. and penetration of 4.5. Air blowing with a catalyst increases the softening point to 230.degree. F. but the penetration obtained, about 8, is still too low for coating grade asphalt. Nevertheless, because such fluxes are relatively inexpensive and available in good supply, the development of methods of modifying these hard fluxes to make them useful for coating grade asphalt is of considerable commercial interest. Various different methods have been proposed for modifying hard asphalt fluxes to meet this need and some of these proposals have been successful in varying degrees. However, there is still a need for a convenient and reliable way of modifying hard asphalt fluxes to obtain coating grade asphalt.
The principal object of the present invention is to provide an effective and convenient method for modifying hard asphalt fluxes so that they can be used as coating grade asphalt. Other objects, including the provision of additional property improvements in the asphalt product of the invention, will also be apparent.